Cost effectiveness of limes
When selecting an agricultural lime to treat soil acidity the total cost needs to be considered. This includes the purchase cost at pit, transport cost to paddock and spreading cost; all factors are converted to 100% neutralising value (NV) for equal comparison and discounted to allow for differences in particle size and speed of reaction.
Sourcing lime from local suppliers, if available, is generally the best option. The further lime needs to be transported, the more critical high neutralising value becomes (Figure 1). The lime supplier should provide up-to-date particle size and neutralising value information that will allow calculation of the best value lime.
Online lime comparison calculator
A useful tool for calculating and comparing the cost effectiveness of agricultural limes is the Lime Comparison Calculator on the Soil Quality website (see Figure 2).
To allow comparison of the total cost per hectare for the equivalent of 100% NV of lime, the Lime Comparison Calculator takes into account:
- cost of the lime
- cost of transport
- cost of spreading
- particle size distribution of the lime
- neutralising value of each particle size.
The neutralising values (NV) of larger particle sizes are discounted using the values of Cregan et al. (1989) to account for the reduced capacity to change soil pH in the short term:
- the NV of particles under 0.5mm is not discounted
- the NV of 0.5-1mm particles is discounted by 50%
- the NV of particles greater than 1mm is discounted by 80%.
The online lime comparison calculator is the easiest way to compare the cost effectiveness of limes. Lime suppliers should provide recent product test results detailing the information required for the calculations. Figure 2 shows lime X compared to lime Y, a coarser lime with lower overall neutralising value. Even though lime Y is 100km closer to the farm, it is still more cost effective to purchase lime X.
Long-hand lime comparisons
The calculations performed by the lime comparison calculator (Figure 2) can be calculated by hand. Here we use are using values for lime X from Figure 2:
1. Calculate the overall percent efficiency of the lime (EP)
Lime EP = Sum all individual particle size EP
EP for the particle size = % of lime × neutralising value (NV) × particle size discount factor
Lime EP for lime X = 86.9 (see Table 1)
| Paticle size (mm) | Particle size discount factor | % of lime | NV | % efficency (EP) |
|---|---|---|---|---|
| 0-0.125 | 1 | 5 | 90 | (5 ÷ 100) × 90.0 x 1 = 4.5 |
| 0.125-0.25 | 1 | 48 | 90.5 | (48 ÷ 100) × 90.5 × 1 = 43.4 |
| 0.25-0.5 | 1 | 38 | 94.8 | (38 ÷ 100) × 94.8 × 1 = 36.0 |
| 0.5-1 | 0.5 | 8 | 72.1 | (8 ÷ 100) × 72.1 × 0.5 = 2.9 |
| >1 | 0.2 | 1 | 62.5 | (1 ÷ 100) × 62.5 × 0.2 = 0.1 |
| - | - | - | - | Overall EP = sum of particle size EP = 86.9 |
2. Calculate the costs
In this example, the lime costs $10 per tonne (t) and needs to be transported 250km to the farm at a cost of 10 cents/km. It can be spread for $8/t.
Costs = lime cost + transport cost + spreading cost
Costs for lime X = $43/t (Table 2)
| Item | Cost/tonne ($) |
|---|---|
| Lime | 10 |
| Transport (at 10c/km/t for 250km) | 25 |
| Spreading | 8 |
| Sum of costs | 43 |
3. Calculate the effective cost of lime on paddock
Effective cost = (100 ÷ EP) × costs
Effective cost for lime X = (100 ÷ 86.9) × 43 = $49.48
For a lime with 100% efficiency, the effective cost would be the same as the actual cost. For a lime with an overall percentage efficiency of 50, the effective cost would be twice the actual cost.
Western Australian lime suppliers
The further lime needs to be transported, the more critical high neutralising value becomes.
Approximately 35 agricultural lime suppliers currently service the WA wheatbelt. A 2008 Department of Agriculture and Food, Western Australia survey found abundant high quality lime sources along the west coast between Perth and Geraldton. The number of sources diminishes moving south of Perth and east across the south coast to Esperance. Limited numbers of inland sources of varying quality are also available.
Many lime suppliers are members of the Lime WA Incorporated group of independent lime suppliers and operate under the association’s Agricultural Lime Industry Code of Practice. Members of Lime WA Inc provide standard product information sheets with detailed product information and independent lime quality test results (downloadable from Lime WA), which can be used with the lime comparison calculator, which is available online on the Soil Quality website.